As a method that realizes secure communications over the Internet, a security architecture for Internet protocol (IPsec) is in wide use.
With regard to encryption using IPsec, an encapsulating security payload (ESP) method is disclosed in NPL 1.
Furthermore, as a method that realizes other secure communication, a secure real-time transport protocol (SRTP) is disclosed in NFL 2. SRTP is an encryption method that results from standardizing a real-time transport protocol (RTP).
Furthermore, in PTL 1 is disclosed a method in which a coverage in which the encryption is performed is adjusted in advance between a transmitting entity and a receiving entity and only one region of a packet that is designated is encrypted.